This invention relates to closures for containers and more particularly to closures and containers having a locking feature so that when the closure is sealingly engaged on a container the cap is locked thereon and can be removed only by special manipulation.
Safety closures are designed to lock into a container in such a fashion as to make their removal difficult, particularly for children. Safety closures are typically used in connection with containers for drugs, medicines, corrosive materials, and the like, which can cause serious injury if opened by children. For example, it is required that certain pharmaceuticals be dispensed from containers provided with safety closures in order to avoid such unintended opening.
In certain cases, however, such as, for example, when the closure and container are adapted for use with harmless substances, it is desirable to provide for the use of the closure in the conventional manner without the safety locking feature. In other cases, it may be desired to utilize a snap lock closure so that the closure is engaged in sealing relationship with the container by a simple downward thrust on the closure.
Several designs for safety closures are available, including single-piece and multi-piece designs. Examples of various designs for closures having a safety locking feature are to be found in U.S. Pat. No. 3,072,276 (Nichols), U.S. Pat. No. 3,360,147 (Shaeffer), and U.S. Pat. No. 2,776,006 (Thornton). A significant problem encountered with prior art safety closures is that of the shear strength of the locking elements. Thus, if the shear strength of the locking elements is too low, the closure can be removed by shearing or breaking away the locking element and this can occur even when manipulated by children. Consequently, it is highly preferred that the locking elements, particularly those on the closure, be integrally formed as part of the closure. Cooke, in U.S. Pat. No. 3,888,376 and U.S. Pat. No. 3,942,899, discloses an improved closure design employing a substantially continuous thread in which the locking means are integrally formed as part of the thread. In this manner, the probability of removing the closure without the proper manipulative steps by shearing the locking means is substantially reduced.
In many cases, however, it is preferred to utilize the closure in a more conventional fashion without the locking feature simply by engaging thread elements of the closure and container and simply torquing the cap into a sealing position or by a simple snap lock. One type of prior art device employs a two-sided closure in which conventional thread elements are provided on one side of the closure for engagement with corresponding thread elements on the inner surface of the mouth portion of the container and the other side provided with lugs which are engageble with corresponding locking elements on the outer surface of the neck of the container. These devices are expensive to manufacture and require the use of excessive amounts of materials in forming the two-sided closure.